Complex hydraulic systems are often used in machines that must apply a large force to a load. Examples of machines of this type are earthmovers, such as front-end loaders and backhoes, and cranes. The hydraulic system functions to transfer power to various portions of the machine. Since these machines are typically used in harsh and/or remote locations, the machines must be reliable and easy to maintain.
A hydraulic system for a heavy-duty machine will usually include one or more linear actuators/hydraulic cylinders, a reservoir, and a high-capacity hydraulic pump that is driven by a powerful motor. The motor may also function to propel the machine. The operator of the machine controls the operation of the machine's hydraulic components through the use of valves that affect the flow of hydraulic fluid to and from said components. The application of pressurized fluid to a hydraulic cylinder in a predetermined manner will cause the cylinder's inwardly-contained piston to move within the body of the cylinder. As a result, the piston rod attached to the piston will be either extended from, or retracted into, the cylinder to cause the desired movement of the machine's member(s) attached to the cylinder.
In a typical hydraulic system, the control valve that is responsible for the operation of any particular hydraulic cylinder is located at a distance from the cylinder. Long flexible hoses and/or pipes are used to connect together the control valve, the cylinder, the pump and the reservoir. Depending on the complexity of the system, additional hoses may be employed between main and pilot valves, and between system check valves and the control and/or pilot valve(s).
One problem with prior art hydraulic systems is that while most of a hydraulic system's components are very durable, they are still susceptible to damage. By the time the pump, reservoir, valves and hydraulic cylinders are connected together, the end result is a large number of hoses, fittings, pipes and valves located in damage-prone areas. Many of these components are difficult and/or expensive to replace. One should also note that not only are the hoses susceptible to being punctured, they can also be damaged through environmental degradation.
Another problem with prior art hydraulic systems is leakage. Not only can each component of a hydraulic system leak, but the fittings that are used to connect together the different components can also leak. At the very least, leakage of hydraulic fluid can pose both safety and maintenance problems. If the machine is used in an environmentally-sensitive location, leakage problems are exacerbated since any leaked hydraulic fluid must be recovered, along with any contaminated soil.
In some hydraulic systems, the use of connecting hoses is minimized by mounting the hydraulic cylinder's control valve, and in some cases, a pump and reservoir, directly onto the side of the hydraulic cylinder. However, this does not substantially avoid having hydraulic components located in an exposed condition where they can be damaged by falling debris or by accidental contact with external structure or formations. This also creates a bulbous, awkwardly-sized unit that cannot be fitted within the closely-packed confines found in many machines.